Try this :D
Turn off the phone, Once the phone is off, Hold the Volume down key then plug the charger (charger should be connected to the power source ",) Once you see the excalmation ( ! ), remove your finger from the button.
Then press the following keys in, Volume Up, Volume Down, Power Key and Volume down. The phone will turn on automatically, this may take several minutes and it will show two gears that are spinning just wait for it to finish.
One more thing all the files on the phone will be deleted but if you have a microsoft account on the phone, check people.live.com to check the contact lists that you have and skydrive for the pictures, that's if you have a microsoft account on the phone.
cheers!